1. Field of the Invention
The present invention relates to an electron emission unit and a flat panel display device employing the electron emission unit. More particularly, the present invention relates to an electron emission unit that may prevent an anode electric field from penetrating a gate electric field so as to avoid arcing, and also may prevent a hazardous voltage being applied to an electron emitting unit and other elements. The present invention also relates to a flat panel display device employing the electron emission unit as a backlight unit.
2. Description of the Related Art
In general, flat panel display devices may be classified into emissive display devices and non-emissive display devices. Examples of the emissive display devices may include a cathode ray tubes (CRT), a plasma display panel (PDP) that may emit light using plasma generated by applying a strong voltage, a field emission display (FED) that may emit light by exciting a phosphor screen with electrons emitted from a plane cathode, a vacuum fluorescent display (VFD) that may emit light by creating thermal electrons through a voltage supplied in a filament and accelerating the electrons by means of a grid so that the electrons may reach an anode to collide with phosphors already patterned and illuminate for displaying information, and an organic light emitting device (OLED) that may emit light by running current through a fluorescent or phosphorescent organic thin film to make electrons and holes meet in the organic layer. An example of the non-emissive display device may include a liquid crystal display (LCD) that may use a liquid crystal that is in a state between solid and liquid and may act as a shutter to selectively transmit or block light according to voltage.
Among these examples, the LCD may be of light weight and low power consumption. However, the LCD may not display an image that is observable in a dark place because it is a light receiving display device and thus the image is produced not by self-emitting but by external light. Accordingly, the LCD may include a backlight unit at a rear side of the LCD apparatus to emit light. In this case, the LCD may also display an image that is observable even in a dark place.
While there may be different backlight units, a linear light source and a point light source may be used as an edge type backlight unit. Particularly, a cold cathode fluorescent lamp (CCFL) having electrodes at both ends of a tube may be commonly used as a linear light source. A light emitting diode (LED) may be commonly used as a point light source.
The CCFL may offer strong white light generation, superior brightness and uniformity, and easy large-scale design. However, the CCFL may operate using a high frequency alternating current. Additionally, the CCFL may operate within a narrow temperature range for light output to occur.
The LED may operate with less brightness and uniformity than the CCFL. This may be especially true in a larger size LED. Also, high power may be consumed when reflecting and transmitting light due to the light source being located on a rear side. Further, the structural complexities of a LED may result in higher production costs. However, the LED may operate using direct current instead of a high frequency alternating current. Additionally, the LED may offer improved power and temperature characteristics, smaller size and longer life expectancy.
Recently, electron emission units employed as backlight units using a planar light emitting structure have been proposed to solve the above-mentioned problems. These electron emission type backlight units may exhibit low power consumption and relatively uniform brightness, even over wider regions, as compared to a CCFL and the like.
For example, an electron emission unit employed as a backlight unit may have an upper substrate and a lower substrate that may be separated from each other by a predetermined gap. A fluorescent layer and an anode may be sequentially disposed on a bottom surface of the upper substrate, and a cathode may be disposed on a top surface of the lower substrate. Also, a stripe-patterned electron emitting unit may be disposed on the cathode.
An exemplary operation of the electron emission unit may include a predetermined voltage applied between the anode and the cathode. Electrons may be emitted from the electron emitting unit disposed on the cathode. The electrons emitted from the electron emitting unit may collide with the fluorescent layer and may excite fluorescent materials in the fluorescent layer, such that visible light may be emitted with extra energy.
However, since the cathode may be formed over the entire surface of the lower substrate, a high voltage directly applied between the anode and the cathode may cause local arcing. Due to the local arcing, the electron emission employed as a backlight unit may not ensure uniform brightness over the entire display surface. Furthermore, the local arcing may damage the anode and cathodes, the fluorescent layer, and the electron emitting layers, thereby shortening the life of the electron emission unit employed as a backlight unit.